Reenforced abrasive wheel and the manufacture thereof



Get. 2, $34 R. c. BENNER ET AL LQYSMYQ REENFORCED ABRASIVE WHEEL AND THE MANUFACTURE THEREOF Filed Sept 30, 1930 2 Sheets-Sheet l INVENTORJ 06L 1934- R; c. BENNER ET AL ,9 0

REENFORCED ABRASIVE WHEEL AND THE MANUFACTURE THEREOF Filed Sept. 50, 1930 2 Sheets-Sheet 2 Patented Oct. 2, 1934 BEENFOROED ABRASIVE WHEEL AND THE MANUFACTURE THEREOF Raymond C. Benner and William G. Soley,

Niagara Falls, N. Y., assignors to The Carborundum Company, Niagara Falls, N. 1., a cor-v poration of Pennsylvania Application September 30, 1930, Serial No. 485,469

13 Claims.

This invention relates to the manufacture of abrasive articles and more particularly to abrasive wheels of the type formed by joining several individual preformed sections together.

The invention is particularly applicable to the manufacture of pulp grinding wheels and other wheels that are too large to be made in one piece. Wheels .of this kind usually require a high power input for operation. Moreover, they are subjected to a wide range of temperature conditions. A pulp wheel, for instance, may be shipped into and used in places where the climatic temperature in the winter time goes well below zero. At the same time under the conditions of their use such wheels are operated in contact with water which is heated to a considerable temperature, even up to its boiling point. It is therefore important that such a wheel not only have amplestrength to stand up under the high power input and the'high surface speed at which it is revolved, but that it should also have a maximum freedom from thermal strains.

Heretofore the most commercially successful pulp grinding wheels made from artificial abrasives have been formed by mounting suitably shaped blocks of bonded abrasive material on metal drums provided with clamping members for holding the blocks in place, or they have been made by joining suitably shaped blocks of bonded abrasive material by means of cement of one kind or another. The former type of wheel requires expensive metal drums and metal clamping members. Moreover, due to the great difference in the coeflicients of thermal expansion of the metal and the bonded abrasive material, such wheels are subjected to serious stresses in undergoing the various thermal conditions to which they are subjected. Wheels which have been made by joining blocks of abrasive material by the use of a suitable cement avoid the disadvantage of requiring the metal drums and clamping devices, and are substantially free from many of the thermal stresses which are set up in a wheel containing a metal drum. However, without the provision of the metal drum there does not exist in the wheel without reenforcement of any kind that margin of safety which is desired in its use for the grinding of wood pulp.

According to the present invention, which constitutes a continuation-in-part of our earlier filed application, Serial No. 252,479, filed February '7, 1928, we reenforce an abrasive wheel made up of several parts cemented together without necessarily resorting to the use of a metal supporting drum. According to our invention this reenchanges in temperature over the range to which the wheel is subject.

The invention may be readily understood by reference to the accompanying drawings in which Figure 1 is a side view of an abrasive annulus constituting one part of the assembled abrasive wheel, according to one embodiment of our invention;

Figure 2 represents a transverse section through a wheel made up of abrasive annuli with reenforcements therein;

Figure 3 is a detail view on a larger scale showing a portion only of adjacent abrasive elements constituting the wheel, toegther with one form of reenforcing body;

Figure 4 is a view similar to Figure 3 of a slightly different form of reenforcing' body;

Figure 5 is a view similar'to Fig. 3 of still another form, this constituting the present preferred embodiment of our invention;

Figure 6 is an end elevation of a wheel similar to that shown in Fig. 1 wherein the annuli are made up of segmental sections;

Figure 7 represents a transverse View in substantially the plane of line VII-V11 of Fig. 8;

Figure 8 is an elevation of a wheel of the type shown in Figs. 6 and "I; and

Figures 9 and 10 are views corresponding to Figs. 6 and 7 of another modification of the invention, Figure 10 being a section in the plane of line XX of Fig. 9.

The general type of wheel to which the present invention relates is illustrated in Figs. 1 and 2 wherein the abrasive wheel 1 is comprised of a plurality of rings or annuli of bonded abrasive material 2 strengthened by a number of reenforcing members 3, 4 and 5, these reenforcing members being in the form of continuous rings or hoops. The. rings or hoops are received in annular recesses provided in the abrasive. By reference to Fig. 2 it will be seen that the reenforcing elements are received in grooves formed in the faces of the annuli. In the adjacent faces of two annuli the grooves are in register, and a single hoop of suflicient width to engage in both grooves is provided. This is shown by the hoop 4 in Fig-. ure 2. Where the grooves are in those faces of annuli which are at the ends of the wheel, the hoops are only half as wide, as shown by the hoops 3 and 5 in this figure. Referring to the hoop 4, it will be seen that it will reenforce both the annuli with which it cooperates.

We have shown three different reenforcing bodies which may be used in carrying out our invention. The first comprises the use of a metal ring, formed of an alloy suitably compensated as to its coeificient of thermal expansion, snugly received in a space provided for it in the abrasive wheel. The metal has a coefiicient of thermal expansion substantially equal to that of the abrasive over the temperature range to which the wheel is subjected. The second embodiment constitutes the use of a reenforcing body comprised partly of metal and partly of a'filling material, the filling material being sufiiciently resilient to absorb any stresses set up by reason of the differences of expansion and contraction at different temperatures. The third type of reenforcement constitutes the use of a metallic body surrounded by an elastic medium and set in a cementitious medium which is less elastic.

The first type 'of reenforcement is disclosed in detail in Fig. 3 wherein grooves 6 and 7 are formed in the adjacent faces of two abrasive bodies 6' and 7'. A continuous metal ring 8 of a metal having the same coefiicient of'thermal expansion as that of the bonded abrasive is accurately fitted into the grooves. A metal which is suitable for use in this connection is a steel having approximately 30.5% nickel. Steels with nickel contents ranging between 30-42% have coefficients of thermal expansion ranging from 1.0 10- C. to 8.0 l0- C. Ceramic bonded abrasives usually have a coeflicient of thermal expansion ranging between 3.5 l0- C. and 6.0x 10- C. Since the metal ring fits accurate 1y into the registering grooves in the abrasive elements, and since the coeflicient of thermal expansion of the metal and the abrasive substantially coincide, the reenforcement will not impose any strain upon the abrasive when the abrasive wheel is chilled to a very low degree, say 40 below zero, or heated to the boiling point of water.

However, instead of providing ooves in the abrasive into which the metal ring will snugly and tightly fit, the arrangement shown in detail in Fig. 4 may be employed. In this case the grooves 6 and '7 in the abrasive members 6 and '7' are made large enough to accommodate the metal ring 8 and a suitable layer of embedding material 9, as clearly shown in this figure.

In such cases we first determine the size of the metal ring we wish to place in the groove and then calculate the size that that ring will attain when it is subjected to a temperature different from the assembling temperature by an amount commensurate with the conditions the wheel will encounter after its manufacture.

If the bonded abrasive has such a coeflicient expansion that a groove into which the metal ring fits accurately under normalconditions will undergo the same change as the metal ring does with a given change in temperature, the layer of embedding material is made of such size and of such material that it will introduce no undue stresses in the bonded abrasive because of its own tendency to change in size when the temperature is changed. However, when the groove does not change in size the same as the metal ring does within a given range of temperatures, the embedding material is made of such thickness and of such material that it will prevent undue stresses from this difference in size as well as from its own tendency to change size. Thus, the coeihcients of expansion of the metal, the abrasive member and the embedding material and the compressibility of the embedding layer as well as the size of the ring are factors that are considered in determining the suitability of a material for embedding the ring and for determining the thickness of the layer of such material to be used to embed the ring.

While metal reinforcing rings may be selected of material whose'coeflicient of expansion closely approximates that of the abrasive, it is impossible to get a metal which has exactly the same coefiicient of expansion as that of the abrasive over a considerable temperature range, and therefore a layer of cement having a modulus of elasticity lower than that of the bonded abrasive which will compensate for even a slight difference of expansion is preferably used to embed such ring in the ring receiving groove.

We have found that a 4 inch layer of a material with a modulus of elasticity of 1.5 X 10 pounds per square inch and a coeflicient of thermal expansion of 20 10* C. around a. ring 42 inches in diameter and 1 inch by 1% inches cross-section of a steel having a coemcient of thermal expansion of 6.0X10-/ C. will prevent undue stresses in an abrasive member comprising ceramic bonded particles of fused alumina which has a coefilcient of thermal expansion of 5.5 x10-/ C. when the wheel is subjected to temperatures between 40 F. and 212 F.

Such a. material comprises Parts by weight Fine silicon carbide (e. g. 500 mesh) 9 Smoked sheet rubber 1 Sulphur 0.25

when cured to the full extent possible with that sulphur content.

Alteration of the composition of the embedding material produces different physical characteristics. The following examples illustrate compositions that are useful with metal rings of sim 'ilar size to that illustrated above but with different coefficients of thermal expansion.

Parts by weight Rubber 1.0 Sulphur 0.225

Inert filler (e. g. 500 mesh silicon carbide)- 9.0

This material, when fully cured, has a coeflicient of thermal expansion of approximately 14x10-/ C., a modulus of elasticity of 1.1x 10 pounds per square inch and a tensile strength of approximately 1500 pounds per square inch.

Parts by 7 weight Rubber 1.5 Sulphur 0.35

Inert filler (e. g. 500 mesh silicon carbide) 8.5

formed of crystalline alumina as the abrasive, we may use the following composition:

Composition Per cent 36-52 grit fused quartz 14. 7 52-74 grit fused quartz 52. 2 74-100 grit fused quartz 13.0 500 grit silicon carbide 7. 8 A" stage phenolic resin 9.0 B stage phenolic resin 3. 3 Benzol-cc per 100 gms. of above 15.

This material possesses the following physical characteristics:

Coefiicient of expansion 5.0 1'0 /C. Modulus of elasticity 1.23 10 #/sq. in. Modulus of rupture 1980#/sq. in. Tensile strength as a joint 1175#/sq. in.

As showing how these physical characteristics may be modified and controlled by a change in the composition of the mixture, we give the following variation as an example:

Composition Per cent 36-52 grit fused quartz 30. 52-74 grit fused quartz 6. 1 74400 grit fused quartz 14.1 500 grit silicon carbide 18.3 A stage phenolic resin 18.3 B stage phenolic resin 13.2 Benzol-cc per 100 gms. of above 0.0

Triethanolamine-cc per 100 gms. of above- 13.

This change in the composition from that given in the first example produces a joint material having the following physical characteristics:

Coefilcient of expansion 5.44X- /C. Modulus of elasticity 0.81 10 #/sq. in. Modulus of rupture 2600#/sq.in.' Tensile strength as a joint 1340#/sq. in.

By reason of the fact that the physical properties of the embedding material, particularly the coeflicient of expansion and the modulus of elasticity, can be controlled in this way, the embedding material can be adjusted to the requirements of the particular abrasive wheel in which it is to be used. Different grades and different grits of abrasives affect the physical properties of the abrasive wheel, and it is therefore desirable that the embedding material shall be adjusted to the composition of the abrasive wheel in which it is used.

It will be noted in connection with the examples above given that the cements have a low modulus of elasticity and will therefore yield readily if the metal ring and abrasive member do not expand at exactly the same rate. At the same time these cements have coeflicients of thermal expansion approximately the same as bonded fused alumina, and will not therefore introduce stresses of appreciable magnitude because of their own rates of expansion.

The following cement has a coeflicient of expansion very close to that of ceramically bonded silicon carbide and it too has a low modulus of elasticity together with the necessary strength:

Composition This material has the following coefllcient of expansion and modulus of elasticity:

Coeflicient of expansion 3.04x10- C. Modulus of elasticity 0.86 10 #/sq. in. Modulus of rupture 1380#/sq. in. Tensile strength as a joint l315#/sq. in.

Fibrous material such as cellulosic material, introduced into the grooves as a pulp, provides compensation for the differential expansion between the metal member and the abrasive body.

The third type of reenforcing body is shown in detail in Fig. 5. According to this embodiment of the invention we cover each metal ring with a layer of compressible material 10 before the ring is embedded in the groove.

The thickness of the compressible material used depends upon its compressibility as well as upon the size and thermal expansivity of the metal member, of the abrasive member, and of the embedding material. Thus, the compressible material must be of such thickness that it offsets the difference between the cross-sectional expansion of the metal ring and the diametrical expansionor contraction of the metal ring, with respect to the abrasive member, and the expansion of the embedding material. Wood veneer or rubber similar to the examples given above may be used for this purpose but we prefer to use a water-proofed vegetable fibre packing material known to the trade as Oilpac. The material 11, used to embed the ring coated with compressible material may be any cement that is compatible with the packing material used, and which has sufficient strength. For example, sulphur, a mixture of sulphur and powdered coke known as Lavasul, resinous or rubber cements may be used with Oilpac coated rings, but sulphur or sulphur cements preferably should not be used with rubber coated rings in wheels that are to be subjected to heat for long periods of time on account of the hardening effect of the sulphur on the rubber.

A suitable material for embedding the ring coated with compressible material is one composed of 22% of a resinous material, such as a phenolic condensation resin known to the trade as Redmanol, inert filler, such as finely divided (200 mesh silicon carbide or low expansivity glass, and 13% of a solvent or plasticizer, such as furfural. A mixture of this nature sets or cures to a strong, hard and somewhat resilient solid when subjected to moderate heating, as for example, at 200 F. for a period of approximately 24 hours.

A filling material that provides resiliency in addition to that of the wrapping on the metal member is one containing rubber. As those skilled in the art will recognize, almost any degree of resiliency may be attained by slight alterations in the composition of the rubber containing material. By way of example, one composition that we have found suitable for this purpose is Parts by weight Silicon carbide fines (e..g. 500 mesh) 9 Smoked sheet rubber 1 Sulphur 0.2

cured to the full extent. Such a material, when properly cured, has a coeificient of thermal expansion of 9.1 10 C. and a modulus of elasticity of 0.15 x 10 pounds per square inch.

In constructing a wheel containing reenforcing bodies we first form an abrasive section with grooves 6 and 7 of the required depth and width and then lay it on its side with the bottom of the upper groove in a level plane. We prime this groove with some of the embedding material softened with benzol, for example, in order to seal the pores, and prevent the embedding material from being drawn into the abrasive body and away from the groove and to promote adhesion. We also prime the upper side of the wheel with thinned cementing material for a similar reason.

The embedding material 11, in quantity slightly greater than that required to completely fill the space between the ring and the groove is then introduced into this upper groove, and the ring 8 with the compressible material 10 attached to its surfaces by an adhesive varnish is then pressed into the thus filled groove.

The surface joining material 12 is then applied to the previously primed upper side of the abrasive annulus 2. The groove and side of another abrasive ring are then prepared in the same manner as just described from the first annulus 2. This second annulus is placed upon the first abrasive annulus with its groove in engagement with the protruding part of the coated metal ring and pressed into position by any suitable means.

The process of adding abrasive rings and metal members is carried on until the desired thickness of wheel is produced. The reenforcing bodies in the end abrasive members need be only one-half the cross-sectional size of those in the interior of the wheel because they do not engage more than one abrasive ring.

One type of cement that is useful in joining abrasive members of ceramically bonded fused alumina with a coefficient of thermal expansion of 5.5 l0- C. comprises 10 parts of rubber, 2 parts of sulphur and 90 parts of finely divided (e. g. 500 mesh) silicon carbide thoroughly mixed and rolled into sheet form. This material, when cured in intimate contact with the bonded abrasive and to the full extent possible with that sulphur content provides a strong joint with a coeflicient of thermal expansion and a modulus of elasticity of such magnitude that the abrasive member will not be strained by the shrinkage of the material upon cooling.

This cementing material and the method of building abrasive wheels comprising a number of annuli without reenforcing bodies is fully described in copending application, Serial No. 484,545.

Instead of using an adhesive material like that just mentioned for the entire joint between each block we sometimes use a space filling and wear resisting material like sulphur or a mixture of sulphur and finely divided coke known as Lavasul" in the outer portions of the joints, that is, those toward the periphery of the wheel, and an adhesive material, such as those described above, in the part of the wheel in the vicinity of the metal rings. sulphur or Lavasul, which does not adhere tenaciously to the abrasive blocks, particularly in the joints between the annuli, we avoid some of the complications arising from differential expansion and contraction between the abrasive material and the joint material.

It will be recognized by those skilled in the art that heat penetrates bonded abrasive structures rather slowly and that the curing of rubber or resinous compositions embedded therein must be controlled accordingly. In some cases, where the rubber composition is both near the surface and deeply embedded in bonded abrasive mate- By the use of such a material as rial, rubber compositions of different curing rates, as modified by the use of accelerators, are used in different parts of the abrasive wheel.

The modifications illustrated in Figures, 6, '7, 8. 9 and 10 show bonded abrasive annuli 2 comprised of blocks 13 of bonded abrasive material joined by a suitable adhesive material that may or may not be the same as used in embedding the metal rings or joining the annuli. These figures show also, a method of mounting a pulp grinding wheel for operation. In these figures, the Wheel 1 is held between two clamping members 14, usually known as flanges, that engage a shaft 15 in threaded relationship in such manner that any tendency of the wheel to turn freely with re-' spect to the shaft causes a further tightening of the grip of thoseflanges on the wheel.

Figures 7 and 8 illustrate a modification in which the metal members are in the form of disks 16, 17, 18, 19 and 20 that engage the shaft and prevent sagging in wheels of relatively great length. The perforations 21 in the disks provide greater shearing strength between the cementing material and the metal member. The resiliency of the cement prevents undue stresses in the abrasive because of differential expansion between the metal and the abrasive.

While specific materials,process steps and physical constants have been used throughout this specification for illustrative purposes, it should be understood that such specific items are not used to limit the scope of the invention. The invention provides means for strengthening abrasive articles without introducing harmful stresses when the abrasive wheel is heated or cooled. To this end the reenforcement, which may be either a single element as shown in Fig. 3 or a composite element as shown in Figs. 4 and 5, should have a relatively low modulus of elasticity if it has a high coefficient of thermal expansion and may have a relatively high modulus of elasticity if it has a coeflicient of thermal expansion approximately the same as that of the bonded abrasive.

By reason of this arrangement a reenforcement can be introduced into the abrasive body after the individual elements thereof have been formed and fired and during the assembling of the individual abrasive elements intothe composite whole. Since the reenforcement is eifectively compensated for temperature changes, so as to impose no strain on the more frangible abrasive material, the factor of safety in wheels of this type is very materially increased, but the cost is much less than the cost of a wheel in which the abrasive segments are clamped on a metal drum.

While we have-described certain specific embodiments and certain particular steps for effecting our invention, it will be understood that various changes and modifications may be made therein.

We claim:

1. In an abrasive wheel, a plurality of bonded abrasive annuli, arranged in ide-by-side rela' tionship and having registering recesses therein, metal reenforcing bodies and a cushioning medium in said recesses in stress absorbing relationship, a single reenforcing body entering the recesses of two adjacent annuli.

2. An abrasive wheel comprising a frangible body of abrasive material having an annular slot formed therein, a metallic ring received in the slot, and an elastic cement bonding the metallic ring with the abrasive.

3. An abrasive wheel comprised of a body of abrasive material formed of' a plurality of sections placed face-to-face, said sections having registering annular channels in the opposed faces thereof forming a continuous annular space surrounded by abrasive material within the body of the wheel, an integral ring in the annular space of sufficient width to be received in both the registering channels which form the annular space, and an elastic cushioning medium interposed between the ring and the abrasive and serving to relieve strains in the structure due to the difference in the thermal expansion of the ring and the abrasive body while intimately connecting the ring and the abrasive whereby the ring will reinforce the body.

4. An abrasive wheel constructed for peripheral grinding comprised of a plurality of abrasive annuli disposed in side-by-side relation, rigid annular metal reenforcing bodies disposed between the adjoining faces of the annuli, said annuli having registering recesses in which the metal reenforcing bodies are received, and means providing a resilient connection between the metal reenforcing bodies and the annuli and capable of compensating for variations in the expansion and contraction of the metal reenforcements and the abrasive material.

5. An abrasive wheel constructed for peripheral grinding comprised of a plurality of abrasive annuli disposed in side-by-side relation, metal reenforcing bodies disposed between the adjoining faces of the annuli, said annuli having registering recesses in which the metal reenforcing bodies are received, and means providing a resilient connection between the metal reenforcing bodies and the annuli and capable of compensating for variations in the expansion and contraction of the metal reenforcements and the abrasive material, said means comprising a layer of resilient material in contact with the metal and a less resilient cement outside the resilient material.

6. An abrasive wheel constructed for peripheral grinding, comprising a plurality of abrasive annuli disposed in side by side relation, said annuli having annular registering recesses in their adjoining faces, a metal reenforcing ring between each of the annuli and extending into the registering recesses, and a cement comprising a phenolic condensation resin and finely divided filler embedding the metal rings in their receiving recesses.

7. An abrasive wheel constructed for peripheral grinding, comprising a plurality of annuli of bonded abrasive disposed in side by side relation, said annuli having annular registering recesses in their adjoining faces, metal reenforcing means between each of the annuli and extending into the registering recesses, and a cement having a modulus of elasticity of the same order of magnitude as but lower than that of the sive material having an annular recess formed therein, a metal reenforcing ring received in the recess, and a cement having a modulus of elasticity of the same order of magnitude as but lower 1 than that of the bonded abrasive embedding the metal'ring in its receiving recess.

10. An abrasive wheel comprising a body of bonded abrasive having an annular recess formed therein, a metal reenforcing ring having a coefficient of expansion approximately the same as that of the bonded abrasive received in the recess, and a cement embedding the metal ring in its receiving recess.

11. An abrasive wheel comprising a body of bonded abrasive material having an annular recess formed therein, a 'metal reenforcing ring having a coeflicient of expansion approximately the same as that of the bonded abrasive material received in the recess, and a layer of cement embedding the metal ring in its recess, the thickness of the cementitious layer and its coefficient of expansion nad modulus of elasticity being so correlated that the cementitious joint does not introduce undue stresses in the bonded abrasive because of its own tendency to change in size when the temperature is changed.

12. An abrasive wheel comprising a body of bonded abrasive having an annular recess formed therein, a metal reenforcing ring received in the recess, and a cement having a coefiicient of expansion approximately the same as that of the bonded abrasive embedding the metal ring in it's receiving recess.

13. An abrasive wheel comprising a body of bonded abrasive having an annular recess formed therein, a metal reenforcing ring having a coeflicient of expansion approximately the same as that of the bonded abrasive received in the recess, and a cement having a coeflicient of expansion approximately the same as that of the bonded abrasive embedding the metal ring in its receiving recess.

RAYMOND C. BENNER. WIL 'IAM G. SOLEY. 

